The present invention is directed to improved drill pipe tester valves and, more particularly, to improved drill pipe tester valves designed to be used above a formation tester valve in a well test string and of the type described in U.S. Pat. No. 4,421,172.
During the course of drilling an oil well, one operation which is often performed is to lower a testing string into the well to test the production capabilities of the hydrocarbon producing underground formations intersected by the well. This testing is accomplished by lowering a string of pipe, commonly referred to as a drill string, into the well with a formation tester valve attached to the lower end of the string of pipe and oriented in a closed position, and with a packer attached below the formation tester valve. This string of pipe with the attached testing equipment is generally referred to as a well test string.
Once the test string is lowered to the desired final position, the packer means is set to seal off the annulus between the test string and a well casing, and the formation tester valve is opened to allow the underground formation to produce through the test string.
During the lowering of the test string into the well, it is desirable to be able to pressure test the string of drill pipe periodically so as to determine whether there is any leakage at the joints between successive stands of drill pipe.
To accomplish this drill pipe pressure testing, the string of drill pipe is filled with a fluid and the lowering of the pipe is periodically stopped. When the lowering of the pipe is stopped, the fluid in the string of drill pipe is pressurized to determine whether there are any leaks in the drill pipe above the formation tester valve.
With the apparatus and methods generally used in the prior art for testing the drill pipe as it is lowered into the well, the fluid in the string of pipe is generally contained within the drill pipe only by the closure of the formation tester valve. In other words, the pressure exerted on the fluid in the drill pipe is also exerted against the closed formation tester valve.
This prior art arrangement has often been utilized with a formation tester valve similar to that shown in U.S. Pat. No. 3,856,085 to Holden, et al assigned to the assignee of the present invention. The Holden, et al formation tester valve has a spherical valve member contained between upper and lower valve member seats.
The Holden, et al formation tester valve is shown only schematically in U.S. Pat. No. 3,856,085, and the details of the mounting of the spherical valve member within the housing of the valve are not thereshown. The actual formation tester valve constructed according to the principles of Holden, et al U.S. Pat. No. 3,856,085 has the upper valve seat for the spherical valve member suspended from an inner mandrel which is hung off an annular shoulder of the outer valve housing, in a manner similar to that shown in U.S. Pat. No. Re. 29,471 to Giroux, and assigned to the assignee of the present invention. The lower valve seat is connected to the upper valve seat by a plurality of C-clamps spanning around the spherical valve member. The lower valve seat member of the Holden, et al formation tester valve does not, therefore, engage any supporting portions of the valve housing.
The spherical valve member of the Holden, et al formation tester valve is held in place within the housing so as to prevent axial movement of the spherical valve member relative to the housing, and is engaged by eccentric lugs mounted on a sliding member which does move axially relative to the housing so that upon axial movement of the lugs relative to the housing, the spherical valve member is rotated relative to the housing to open and close the valve.
When pressure testing drill pipe located above a formation tester valve like that of Holden, et al, experience has shown that excessive pressure exerted upon the top surface of the spherical valve member of the Holden, et al apparatus, causes the spherical valve member to exert a downward force on the eccentric lugs thereby shearing the eccentric lugs off their carrying member. This severely limits the maximum pressure which may be exerted upon the fluid within the drill pipe to pressure test the same, and it is particularly a significant problem in very deep wells where the mere hydrostatic pressure of the fluid within the drill pipe is relatively high. It has been determined that the maximum differential pressure which can safely be carried by the Holden, et al valve is about 5000 psi.
Another prior art valve having a spherical valve member which does not move axially relative to its housing is the subsea test tree valve shown in U.S. Pat. No. 4,116,272 to Barrington.
Other prior art valves having a spherical valve member which does move axially relative to the housing are shown in U.S. Pat. No. 4,064,937 to Barrington; U.S. Pat. No. 3,568,715 to Taylor, Jr.; U.S. Pat. No. Re. 27,464 to Taylor, Jr.; U.S. Pat. No. 4,009,753 to McGill, et al; and U.S. Pat. No. 3,967,647 to Young.
A drill pipe tester valve which may be run in the well test string directly above a formation tester valve such as that of Holden et al, U.S. Pat. No. 3,856,085, is shown in McMahan et al, U.S. Pat. No. 4,319,633. While such a drill pipe tester valve has a spherical valve member which can withstand high differential pressure thereacross, the spherical valve member may be opened prematurely through the application of force to the lower adapter when lowering the well test string into the well bore.
The drill pipe tester valve described in U.S. Pat. No. 4,421,172 provides a drill pipe tester valve which is run in the well test string directly above a formation tester valve such as that of Holden et al, U.S. Pat. No. 3,856,085. This drill pipe tester valve overcomes the difficulties encountered due to pressure testing directly against the formation tester valve. The drill pipe tester valve has a lower valve seat which is supportably engaged by the valve housing, so as to prevent downward forces from being exerted upon the eccentric actuating lugs thereof when the fluid in the drill pipe is pressurized, thereby preventing the shearing of those lugs on the drill pipe tester valve. The drill pipe tester valve can withstand differential pressures up to 10,000 psi. The drill pipe tester valve further includes a resilient spring to prevent movement of the spherical valve members to its open position until a predetermined force is applied to the drill pipe tester valve.
However, the drill pipe tester valve described in U.S. Pat. No. 4,421,172 suffers from the problems of either bypass seal cutting during closing of the bypass when the ball valve is opening before the completed closing of the bypass seal or the creation of a pressure trap requiring compression of the fluid between the closed ball valve in the drill pipe tester valve and any closed tester valve run therebelow when the bypass seals are completely closed before the opening of the ball valve in the drill pipe tester valve.